The acidification of the oceans, expected to result from rising atmospheric carbon dioxide levels, could dramatically increase the number of fish larvae deaths in some species, scientists warn.

Some larval fish use their sense of smell to detect predators and navigate their way toward the correct habitat. But previous studies have shown that acidification of water by CO2 can interfere with these survival tactics. For example, clownfish larvae (Amphiprion percula) actually become drawn to predator signals when reared under more acidic conditions.

To find out how much of a risk this behavior posed, a team studied the larvae of clownfish and damselfish (Pomacentrus wardi). At normal CO2 levels, both fish species avoided the scent of predators. But at higher CO2 concentrations of 850 parts per million, the clownfish and damselfish stayed near the predator signal more than 90 percent of the time.

The researchers then released damselfish into coral reefs. Larvae raised under the high-CO2 treatment took more risks such as straying from the reef, the team reports in the Proceedings of the National Academy of Sciences. And they were 5 to 9 times more likely to be killed by predators as larvae raised under normal CO2 levels. If similar patterns are found in other species, the authors write, “the effects of rising atmospheric CO2 on marine biodiversity will be profound.” – Roberta Kwok